Henk_v wrote: β02 Mar 2023, 23:59
ringo wrote: β02 Mar 2023, 22:22
Henk_v wrote: β02 Mar 2023, 21:34
I have a shoe here fearing for his future. I hope more pictures arrive...
Regarding the pins on the caliper; at the temperatures the brakes run, heat exchange by radiation can exceed convective heat exchange. Fins are terrible at radiating as most of the surface radiates towards the neighboring fins. I can imagine the shroud being of conductive material and having pins too. The pin spacing seems to imply this. Heat will then be transferred to the shroud by radiation and is convectively transferred to to the cooling air by the shroud pins. This could mean the shroud runs a bit cooler, which may be a desirable effect.
Maybe you are confusing what is happening. The convection is of the air blowing past the pins.
Radiative heat transfer usually has to do with light emission, such as fire etc. Once the view of that light or radiation, be it IR or whatever is blocked by a body then you are mostly depending on convection to transfer heat behind the shadow of that body.
Fins are not terrible for heat transfer. That's why radiators in most applications have fins and not studs.
Both have their strengths and weaknesses, usually with studs, it's for mechanical reasons why they are selected.
I design heat exchangers for a living. I hope I'm not confused...
I am not at all saying fins are terrible. They are just not the best for radiative cooling. Fins are great if the limit of heat exchange is in the thermal conductivity of the exchanger. They provide a low resistance way of exposing area and a large conduction path.
If you look better at radiators, you'll discover that high performance radiators are often a hybrid between pin and fin. The fins are perforated and skewed to make many small fins to mix the airflow and break the boundary layer.
In aluminium the thermal conductivity is not a limiting factor and pins can(can!) be effective in keeping boundary layers at bay and mixing the airflow at the cost of some additional resistance.
Air is terrible at absorbing radiation. The radiation of the sun needs about 16 km of atmosphere and some stuff in it to be attenuated enough to make earth livable,
Absorbing the heat radiation with another body with a low emissivity and convectively transferring that heat to the air can be a great way to make the heat exchange to the air more effective and could potentially keep the shroud cooler. A cooler shroud may give an opportinity to use lighter non-metallic composites near it reducing weight (allthough I realise that is quite an hypothesis)
Well in reality in the feild. Fins are more efficient. It seems you do design in theory or for research. You are talking about radiation only.
I'm in oil and gas engineering for over 10 years. I don't specialize, i dabble in a lot of equipment design. Pin extended surface exchangers are much bigger. Less heat exchange simply down to less surface area. I am sure you can work out some surface area calcs and see for yourself. Also there are some phenomena in reality that you are limited by such as fin/stud tip temperatures.
Studs/pins are usually used over fins because they are more resistant to fouling and corrosion and theyre mechanically stronger. 90% of the time we use fins for convective heat exchange. Studs are special case. And explains why you will see most radiators, especially in automotive applications having fins. Case in point the same F1 radiators. Convection between air and metal surface.
And again There is mostly convective heat exchange in that area on the brake. Not radiation. With radiation you usually have more than enough heat flux to not need to use fins or pins, the bare surface is sufficient.